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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/IUFQRSMIEBKZO3O2L3PLPIKIHGY7V4QM/?format=api",
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    "message_id": "80F55B8DC03341DEA20C7B6465578802@ACER2008",
    "message_id_hash": "IUFQRSMIEBKZO3O2L3PLPIKIHGY7V4QM",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/XW5CKUYDKDAVO6UEVEEP5OXDSJYJPW7T/?format=api",
    "sender": {
        "address": "tdcarrell (a) gmail.com",
        "mailman_id": "5bb2545c6988476e93847c27ced55d07",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/5bb2545c6988476e93847c27ced55d07/emails/?format=api"
    },
    "sender_name": "Terry Carrell",
    "subject": "[amsat-bb] Re: some exceedingly clever technology",
    "date": "2011-08-28T22:45:08Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/OKTCJWUBPFXSSZ7G7NKQBBBIW4KJTXXC/?format=api",
    "children": [],
    "votes": {
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        "status": "neutral"
    },
    "content": "This is what the KiwiSAT - ADAC - experiment will investigate.\nhttp://www.kiwisat.org/science.html\n\nTerry, ZL3QL.\n\n----- Original Message ----- \nFrom: \"Phil Karn\" <[email protected]>\nTo: \"R Oler\" <[email protected]>\nCc: \"Amsat BB\" <>\nSent: Saturday, August 27, 2011 4:54 AM\nSubject: [amsat-bb] Re: some exceedingly clever technology\n\n\n> On 8/24/11 8:11 PM, R Oler wrote:\n>>\n>> http://onorbit.com/node/3709\n>\n> Thrusters are necessary for orbit control, but for attitude control\n> (which I think we really need) you'd *really* prefer something that\n> doesn't consume a fuel.\n>\n> These attitude control systems come in basically two types:\n> magnetorquers and reaction wheels. Magnetorquers exchange angular\n> momentum with the earth by acting on its magnetic field, but they tend\n> to be slow, imprecise and require complex control and sensing systems\n> including a magnetometer far enough from the spacecraft to get away from\n> its own magnetic fields.\n>\n> Reaction wheels come in two kinds: momentum wheels and control moment\n> gyros. Momentum wheels change speed while control moment gyros don't.\n> The latter seem much more common in spacecraft but I'd investigate both.\n> They're good for quick, accurate pointing like you'd need to keep an\n> antenna pointed down or a solar panel pointed at the sun.\n>\n> Having both a magnetorquer and a set of wheels can be advantageous as\n> the magnetorquer can be used occasionally to dump accumulated angular\n> momentum from the wheels should it build up from small external torques.\n>\n> Controlling attitude also means measuring it, and for this I keep\n> thinking about small, cheap CCD video cameras. If we could build good\n> enough sunshades we could snap pictures of star fields and look them up\n> in a database. If you can match multiple stars in an image, then a\n> single image could fix the attitude of the spacecraft. But I'd want to\n> put a camera on each surface if possible. They could also sense the sun\n> and the earth, though that's not as simple as it might seem. The sun\n> usually overloads a CCD and produces streaks while the earth is very\n> large in LEO. It might be possible to recognize the limb of the earth\n> and get better precision that way. A lot would depend on the software\n> processing these images, and it would be a challenge to write.\n>\n> -Phil, KA9Q\n>\n> _______________________________________________\n> Sent via [email protected]. Opinions expressed are those of the author.\n> Not an AMSAT-NA member? Join now to support the amateur satellite program!\n> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb\n\n",
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}